Thanks JohnD - also to Cremeeg and RF Lighting. Your comments suggest that with a PME earth, RCD protection would not be required if all circuits are individually protected by RCBOs. Why the difference?
In any event I will try a time delayed RCD in the first instance and also inquire about...
Right now I have an ancient Consumer Unit with all circuits, i.e. the whole installation, protected by a single 100ma RCD - which invariably trips during an electrical storm causing much annoyance - and thawed freezers when we're away. I was intending to have the consumer unit replaced and have...